A quarter-century ago, then-Senator Sam Nunn, Democrat of Georgia, pretty much doomed former senator John Tower’s chances of becoming defense secretary for the first President Bush.

Thursday, now-former senator, and anti-nuclear activist, Nunn will do what he can to push another former Republican senator, Chuck Hagel of Nebraska, into the defense secretary’s cavernous Pentagon E-ring office.

Nunn’s dual roles highlight Senate clubiness – and the difference between the two nominees.

— In 1989, there were persistent, and legitimate, questions surrounding the dapper Tower’s treatment of women, and his fondness for alcohol. The Senate ultimately voted 53-47 against confirming the ex-GOP senator from Texas, marking the first time a newly-elected president had been denied a Cabinet officer.— In 2013, there are no indications that Hagel is saddled with any such baggage. But there is a dedicated core of pro-Israel conservatives and largely GOP hawks who find Hagel’s views on defense and the Middle East so extreme they are doing everything they can to keep him out of that E-ring office.

Perhaps that’s why Nunn, and former Republican Virginia senator John Warner, are expected to introduce Hagel to the Senate Armed Services Committee. Nunn is a former chairman of that panel — he was in charge when it rejected Tower — and Warner became a member, after serving as Navy secretary. The committee begins its confirmation into President Obama’s nomination of Vietnam veteran Hagel to run the Pentagon Thursday morning.

Hagel, responding to written questions from the committee, basically recites Pentagon talking points on the issues of the day, ranging from Iran (“The next Secretary of Defense must be vigilant in pursuing the goal of preventing Iran from acquiring a nuclear weapon, and must maintain our unshakeable commitment to Israel’s security”) to Afghanistan (he punts on how fast U.S. troops should leave over the next two years) to women in combat (he pledges to act ” expeditiously” to carry out the Pentagon’s recent decision to open virtually all combat billets to them).

U.S. Senate

John Tower, then

Tower never forgave what he saw as Nunn’s underhanded effort to derail Tower’s 1989 nomination.

“At the time [Nunn] arrived at the conclusions that the president’s nomination was ill-advised and that it was his duty to oppose confirmation, rather than resorting to hints, leaks to the news media, and stalking-horses, he could have personally informed me of his views,” Tower wrote in his 1991 memoir, Consequences. “At the very least, I would have had a chance to see and hear for myself that Nunn’s decision was irreversible.”

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Sam Nunn, now

Tower never got to elaborate on what he meant by that passage, because he died in a plane crash shortly after the book’s 1991 publication. So it fell to his ghostwriter, Roger Gittines, to explain what, or who, Tower blamed for his defeat.

I think he saw Sam Nunn as playing the pivotal role in shooting him down. He couldn’t understand why Nunn had done it, other than simple ambition and ego. What really bothered him was that Nunn didn’t play by the rules, that there’s an institutional ethic involved that Tower honored because he had spent 25 years in the Senate. He saw Nunn’s actions damaging the Senate, and the institutional process that is vital to building trust and loyalty among its members being shattered, because Sam Nunn, perhaps, wanted to be president of the United States and he was willing to do whatever he had to do to accomplish that end.

Tower’s written words, self-serving as they may be, are worth recalling. He cited “hints, leaks to the news media, and stalking-horses” for his defeat. That’s pretty much the arsenal Hagel opponents are now wheeling out, like so many ancient artillery pieces, aimed squarely at his nomination.

They’ve lit the fuses, which have been sputtering for weeks now. Thursday we learn just how much is firepower, and how much is fizzle.